Fireflies and Raytracing noise with Movie Render Queue

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Not too long ago I posted this Raytraced Reflections Without Temporal Anti Aliasing thinking that I’d found a fix but after encountering fireflies and noise again it seems like that fix was more context specific and that there’s a much broader issue that extends beyond just reflections.

The bottom line is that when rendering a sequence out of the Movie Render Queue you can sometimes get fireflies and noise particularly in the reflections. This of course is a common issue with 3D rendering in general beyond Unreal Engine but usually there’s solutions to mitigate or remove them either within the rendering process or in post.

Currently the only “fix” that seems to eradicate all fireflies and noise in the reflections as far as I know is leaving on TAA in the Anti Aliasing section when rendering. If you’re still using spatial or temporal samples TAA will still need to be enabled for both the fireflies and noise to be gone, this of course is not recommended for various reasons but aside from the issues that TAA can introduce such as ghosting, it has a noticeable downgrade in image quality which is a big reason to even use these multisampling anti aliasing features in the first place so it’s kind of counterintuitive.

So far I have experienced a lot of noise in the reflections which is unaffected by the amount of samples I use whether that be from the spatial/temporal samples or directly increasing the reflection samples per pixel itself. Disabling or enabling the raytracing denoisers also seems to have little effect on the noise.

r.RayTracing.GlobalIllumination.FireflySuppression exists for global illumination and it seems to work for removing the fireflies for the most part. I’ve also come across fireflies in the World Depth when rendering out different passes. Another thing to note is that disabling the Tone Curve will make the fireflies significantly worse in most cases and when bloom is enabled it picks up the fireflies and noise in the reflections which leaves you with a lot of bright flickering.

I don’t get fireflies occurring on every render but only some and the seemingly random nature of when I get them makes trying to systematically reproduce them difficult. Hopefully I can bring awareness to this because its quite a big deal when working with Unreal Engine for cinematics!

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Hey,
I read this post so many times and also tried to solve this issue and I got something that helped me a ton.

  1. Select all the lights in your scene and bump up the sample count from 1 to 4 or 8. This reduces the noise significantly!

  2. Ramp up the sample count for reflections and translucency in post process volume to 12 or even 24.

I after playing with the raytracing settings for hours I realized that the noise in the reflections was only a fraction of the problem. Most of the noise was introduced due to the way I set up my lights and the low sample count on them. I hope this helps.

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Raising samples will definitely improve noise but a lot of the time won’t exactly do much to solve fireflies as they generally seem to be caused by some unpredictable instabilities in the render process so generally you’d want to clamp the values out or such. Anyway it’s been awhile since this post and a lot about UE has changed of course so I’ve been using lumen instead of the raytraced features but if I come across them I generally just leave on TAA (can’t speak for TSR on UE5) since it seems to have some feature which removes them or I try to remove them in post.

Now, if I made a thread about all the issues I’m having with Lumen however… :wink:

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Has there been any improvements on this? Anybody find a solution to the fireflies? I cant get rid of them, its driving me nuts and I’m on a deadline smh

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Like I said above I haven’t been using the standalone raytraced features in UE5 aside from the RT shadows (which also has a pretty good replacement by using RTXDI through the Nvidia branch of Unreal) because they all are “deprecated” and don’t seem like they will ever receive future improvement since the goal now is on Lumen or the Path Tracer. As for the fireflies unfortunately I don’t believe they were solved if they were caused by the standalone RT features. You’re better off switching to the Hardware RT Lumen or using the Path Tracer. That being said I have another can of worms to open when it comes to issues facing Lumen and TSR. Anyway your problem might still be solvable depending on the context so if you wanna explain in more detail perhaps could be of use.